Electronic image scanning systems have been introduced for automatically scanning an exposed storage phosphorous element to generate electronic data representative of an image. The scanning systems incorporate a read unit that photoelectrically detects an image formed by scanning the storage phosphorous element with a stimulating radiation. Once scanned by the reading unit, the storage phosphorous element is erased by an erase unit for subsequent use.
It is desirable to locate the storage phosphorous element, for example a film sheet or plate, within a protective cassette for handling purposes. U.S. Pat. Nos. 5,310,059 and 5,276,333 issued to Robertson, for example, illustrate cassettes for use with an x-ray storage phosphorous plate. A hooked extractor of the type described in U.S. Pat. No. 5,330,309 issued to Brahm et al., incorporated herein by reference, is used to extract the storage phosphorous plate from the cassette for presentation to a read unit and erase unit of a scanning system as described above. Once erased, the storage phosphorous plate is inserted back into the protective cassette.
In order to improve processing efficiency, an autoloader device has been developed to automate the presentation of a plurality of cassettes to the extractor, thereby relieving the operator of the tedious task of loading individual cassettes. For example, U.S. Pat. No. 5,328,019 issued to Boutet et al., incorporated herein by reference, discloses an autoloader mechanism that utilizes cog belts to index a plurality of cassettes to a read site for extraction. A pinch roller drive assembly is used to advance the cassettes at the read site into a cassette clamping mechanism, for example of the type disclosed in U.S. Pat. No. 5,315,632 issued to Flynn et al., incorporated herein by reference, so that the hooked extractor described above can extract the storage phosphorous plate from the protective cassette.
One drawback to the use of the abovedescribed autoloader is that the cog belts are designed to accept a specific size cassette. It is common in the medical imaging field, however, to utilize cassettes of varying sizes for different imaging applications. In order to accommodate different sized cassettes, the cog belts are designed with a horizontal separation distance that accepts the largest of the cassettes to be utilized and smaller cassettes are then placed in a pallet having dimensions equivalent to the largest cassette. The pallets are then loaded in the autoloader in the same manner as the largest cassettes.
The use of the pallets requires additional manual operations for the operator and creates storage problems when the pallets are not being utilized. Accordingly, it would be desirable to provide an autoloader that automatically indexes cassettes of varying sizes without requiring the use of a pallet.